This invention pertains to lubricants and, more particularly, to an adhesive, friction-reducing grease particularly effective for lubrication of the interface between the side of a railroad track and the wheel flanges of trains.
Lubrication of the sides of railroad tracks has been practiced by the railroad industry for the last 50 years. Until recently, such practice was limited to areas of the track where curves existed. It is in such curved track that the wheel flanges can come into more direct contact with the track sides. The application of a lubricant to the track sides before the curve and the action of the train wheels to spread the lubricant along the track through the curved portion provides friction reduction and reduced track and wheel wear.
However, numerous studies done within the last ten years have shown that significant additional benefits can be achieved if the tangent (straight) as well as curved track is lubricated. The reasons for this are not completely understood but are believed, at least in part, to be due to a less than perfect parallel alignment of wheels and track which exists on most if not all trains.
One benefit of increased lubrication of railroad track sides is further reduction in frictional drag at the track side/wheel flange interface. Reports from various railroads indicate that this additional friction reduction can result in between 10% and 30% fuel savings. Other benefits of increased lubrication of railroad track sides include reduced track and wheel wear, and reduced noise levels in urban settings.
There are three common methods to apply the lubricant to the railroad track side. The oldest method is the wayside lubricator. This device comprises a sealed reservoir of lubricant near the track. Connected to this reservoir is a length of piping to convey the lubricant to some manner of nozzle or other applicator on the track side. When a train begins to pass over that portion of track, a sensor is activated and lubricant from the reservoir is pumped out the nozzle. Each set of wheels commonly gets a shot of lubricant which is then spread down the track. The wayside lubricator was the main method of application when only curved track was being lubricated. The disadvantages of wayside lubricators are that they are usually in remote areas and therefore require special trips by service personnel when malfunctions occur. Because they are constantly exposed to the elements, malfunctions occur frequently.
The second method of application of lubricant to the railroad track side is by a special mobile applicator. This mobile applicator can be a two-wheeled trailer type apparatus connected to the back of a rail inspector's truck. Sometimes the apparatus is mounted in the payload area of the rail inspector's truck. In either case, as the rail inspector drives his truck down the railroad track inspecting the rails for excessive wear or fatigue failures, the apparatus applies the lubricant to the track sides and also assists in spreading it down the track. While this method does not suffer from the disadvantages of the wayside lubricator, it does require special equipment which is utilized on trips not made by railroad trains.
The third method of application of lubricant to the railroad track is by using equipment that is on board the train locomotive itself. The components of the on-board lubricator are in the most general sense similar to that of the wayside lubricator: a lubricant reservoir, application nozzles, and piping to convey the lubricant from the reservoir to the nozzles. Each nozzle is positioned in near proximity to one of the locomotive's wheel flanges and is designed to provide a spray pattern of lubricant to the wheel flange as the train is moving. The wheel flange spreads the lubricant to the track side and down the track as the train moves. Most frequently, when the on-board lubrication system is operating, a metered amount of lubricant is fed to the nozzle per length of track. Some more advanced on-board lubrication systems also have a curve-sensing device. This device detects when the train is traveling over a curved portion of track and automatically increases the amount of lubricant being metered out to provide additional friction reduction and wear protection. Although on-board lubricators are a capital investment for each locomotive, they have many advantages not realized by other methods and are rapidly growing as a method of choice for application of lubricant on railroad track sides.
Given a particular method of application to the sides of the railroad track, the level of benefits achieved will depend on the properties of the lubricant used. Several properties are desirable for a high performance railroad track/wheel flange lubricant. The lubricant should have sufficient pumpability and mobility so that it is easily applied by the nozzle. Once applied the lubricant should transfer from the wheel flange to the rail side without fling-off. The lubricant should have excellent adherence properties which allow it to remain on the rail side, be spread far down the track, and not migrate to the top of the rail. Once on the rail, the grease should resist being washed off by water (rain) so that several trains can pass over it before relubrication is required. This combination of adhesion, spreadability, and water resistance as they apply to a railroad track/wheel flange grease is sometimes referred to as retentivity. The railroad track/wheel flange lubricant should have minimal oil separation (bleed) characteristics. It is believed that the contact pressure between the rail side and the wheel flange can become as high as one-half million pounds per square inch. Accordingly, the railroad track/wheel flange lubricant should have excellent extreme pressure (EP) and antiwear (AW) properties. The lubricant should most desirably provide this EP/AW characteristic without being corrosive to ferrous metals. Instantaneous contact temperatures at the railroad track/wheel flange interface have been estimated in excess of 350.degree. F. Any lubricant which is corrosive to the rail surface at such temperatures may, over many train passes and long periods of time, promote corrosive fatigue of the rail. This is particularly serious since rail fatigue is a major cause of train derailments. Finally, since this lubricant is being applied on railroad tracks which network the entire country, the lubricant should be environmentally acceptable.
Over the years, a variety of lubricants have been used and suggested for use to lubricate the railroad track/wheel flange interface. Most of these lubricants have been greases, due in part to their superiority of application without fling-off. These greases are typified by the well known group of greases which comprises a thickener of simple fatty acid soap salts of calcium or lithium and further comprise graphite and/or molybdenum disulfide as extreme pressure and antiwear additives. Also suggested are stable mineral oil (base oil) dispersions of graphite and/or molybdenum disulfide such as those found in U.S. Pat. No. 4,634,545.
These products, while having provided a certain degree of success, do have shortcomings with respect to the above-mentioned properties. In particular, greases or mineral oil dispersions which contain graphite are often limited in their level of EP/AW performance. This is because the graphite most commonly used in such products is a material commonly known as amorphous graphite. The term amorphous graphite is technically a misnomer since such material is virtually devoid of the extended laminar, hexagonal carbon arrays necessary for true graphitic structure. Amorphous graphite is usually about 75% carbon and about 25% abrasive oxides of silicon, aluminum, and iron. Instead of providing high levels of EP/AW performance, amorphous graphite is extremely abrasive. The main reason for its widespread use in lubricants appears to be its very low cost. More expensive synthetic graphites or highly pure natural graphites (with true graphitic structure) are superior to amorphous graphite as lubricity additives. However, even these materials have significant levels of abrasive oxides of silicon, aluminum, and iron. Furthermore, although these graphites are fairly effective as AW additives under low loads, they are limited in their ability to perform under high loads. Another disadvantage of graphites is their corrosivity at high temperature. The reason for this is most likely due to the presence of adsorbed, corrosive impurities. In any event, even purified graphite will exhibit this distinct corrosive nature, as easily demonstrated by high temperature copper corrosion testing of the corresponding lubricant.
Railroad track/wheel flange lubricants containing molybdenum disulfide suffer from similar deficiencies. Molybdenum disulfide, in its purified form is relatively free from abrasive contaminants and is generally superior to graphite as a wear prevention additive at low loading levels. However, at high loads, the performance of molybdenum disulfide rapidly decreases. The sulfur content of molybdenum disulfide makes it quite corrosive in lubricants at temperatures such as 350.degree. F. Also, the fundamental presence of the heavy metal molybdenum makes such lubricants increasingly unattractive from an environmental viewpoint because it can be harmful to plant life and animals. Finally, molybdenum disulfide is very expensive, making its use in lubricants costly.
It is, therefore, desirable to provide an improved railroad track/wheel flange grease which overcomes many, if not all, of the preceding problems.